1. Field of the Invention
The present invention relates to an autofocus camera having a multipoint focus detecting system which can detect a focus state (an amount of defocus) at each of a plurality of focus-measuring points.
2. Description of the Prior Art
In conventional AF (autofocus) cameras, a phenomenon known in the art as “cosine error” tends to occur because the focus detecting system has, at most, one to three focus-measuring points. If the lens is swung by an angle θ to recompose after an in-focus state is achieved on the central focus-measuring point positioned substantially at the center of the picture plane seen in the viewing area of the viewfinder, a focal point deviates rearwards from the previous in-focus point by cos θ of the swung angle θ or (1-cos θ) times the object distance. This phenomenon is known as cosine error. Cosine error becomes noticeable especially in a wide-angle lens, i.e., a lens of short focal length. This is because the wide-angle lens tends to be swung by a large angle because of a wide field of view of the lens. Namely, cosine error seldom becomes a substantial problem in a telephoto lens, i.e., a lens of long focal length. In addition, cosine error tends to occur when the depth of field is small, e.g., when an iris diaphragm of the lens is widely open. Namely, cosine error seldom becomes a substantial problem when the depth of field is great.
Many AF cameras developed in recent years are equipped with a multipoint focus detecting system so that focusing is automatically achieved with a high degree of precision to satisfy photographers' demand. In such multipoint AF cameras, there is little possibility of cosine error becoming a problem because the lens seldom needs to be swung after focus is achieved.
In a multipoint AF camera, when the user selects a focus-measuring point from a plurality of focus-measuring points that are generally represented by a plurality of small frames (focusing sections) superimposed on the object image seen through the viewfinder. When the user selects a focus-measuring point of interest from the plurality of focus-measuring points, he or she operates a select button or knob to select the corresponding focusing section while viewing the same.
However, specifically when the number of focus-measuring points is great, it is troublesome for the user to select one focusing section from a great number of focusing sections because they need to move the focusing section of interest step by step by operating the select button.